1. Field of the Invention
This invention relates to superconductive photoconductive-substance of the La-Cu-O system defined to be photoconductive, substance correlative with superconductivity whose composition is outside but includes even areas continuously close to that of regular oxide superconductors. Experiments on the optical properties, especially on the photoconduction in response to high-speed pulses, e.g. a pulsed light out of a dye laser, of substance with a chemical formula of La.sub.2 Cu.sub.1 O.sub.z have revealed an unexpected correlation between the superconductivity and the photoconductivity of the substance. The invention also relates to a method for producing the above-mentioned substance. When the substance is cooled very quickly, it becomes a photoconductive semiconductor. On the other hand, when the substance is cooled slowly, it becomes a photoconductive superconductor. The substance in the invention is expected to be useful in developing new industrial field of "Superconductive Opto-Electronics".
2. Related Art Statement
There has been no publications on such a system of substance which has superconductive photoconductivity or both superconductivity and inherent photoconductivity.
Conventional superconductors are metals or alloys in the main. Recently, much attention has been paid to high-temperature oxide superconductors, such as superconductors of the Y-Ba-C-O group, and considerable amounts of additives such as barium (Ba) and strontium (Sr) are used to raise the superconductive critical temperature (T.sub.c). Studies and measurements on the optical properties of the superconductors at and in the proximity of visible wavelengths have been limited to the study of reflection and scattering of light therefrom due to a part of the metallic properties of such substance.
It has been believed that light is simply reflected from or scattered by the surface of a superconductor and is not allowed to enter therein. Study of optical properties, except the phenomena of reflection and scattering, has been treated as a completely different field from that of superconductivity in academic institutions, domestic and abroad, and in international conferences.
On the other hand, if any substance having superconductive photoconductivity or both superconductive capability and photoconductive capability is produced, a number of new electronic and optoelectronic devices may be developed; for instance, a superconductive phototransistor, a "superconductive optical computer" with a combined characteristics of the "superconductive computer" based on the currently studied Josephson devices and the "optical computer" proposed in optoelectronics, "superconductive optical fiber", and the like.